SUMMARY A critically important feature of the brain is the ability to generalize from previously encountered stimuli to new stimuli. Generalization allows the brain to reduce computational demands that would otherwise be necessary to create unique representations for each and every encounter, while enabling animals to deal with the complexity of real-world situations. Stimulus generalization is a fundamental cognitive mechanism that underlies adaptive behavior. While generalization reduces the necessity of learning the associative value of every stimulus we encounter, equally important is the ability to distinguish perceptually related stimuli that hold different meanings. The neural mechanisms underlying the shift from discrimination learning to generalization remain poorly understood. The research proposed here aims to examine olfactory fear generalization and discrimination on multiple levels. In Aim 1 I will use a novel functional MRI (fMRI) paradigm of olfactory aversive conditioning to associate odor cues with an aversive outcome to explore the behavioral, physiological, and neural mechanisms underlying olfactory generalization. Then, in Aim 2 I will use repetitive transcranial magnetic stimulation (rTMS) techniques to modulate olfactory generalization gradients to identify the specific functional roles of brain regions involved in generalization. The research proposed here will help delineate the neural and behavioral underpinnings of odor generalization in limbic brain areas (hippocampus, amygdala, orbitofrontal cortex, and piriform cortex) known to be involved in regulation of emotion and decision-making. Thus, findings emerging from my project could inform future translational studies in patients with anxiety or post-traumatic stress disorder (PTSD) whose symptoms may arise from disruptions of stimulus generalization, and may help direct new treatments or insights into diagnosis and prognosis.